The present embodiments relate to shear wave imaging. Ultrasound may be used to detect a shear wave in tissue.
Shear is a viscoelastic property of tissue. The shear wave velocity of tissue may indicate useful information about the health of the tissue. Shear wave images may be generated. A characteristic of the shear wave in the tissue is determined for different spatial locations. An image of the characteristic as a function of space is generated. However, a large number of transmissions and receptions are used to estimate shear wave information in a large region, resulting in a slow frame rate.
Another tissue property or component of viscoelasticity is elasticity. Ultrasound imaging may operate in an elasticity imaging mode. U.S. Pat. Nos. 5,107,837; 5,293,870; 5,178,147; and 6,508,768 describe methods to generate elasticity images using the relative tissue displacement between adjacent frames. The tissue strain is determined in response to a stress applied to tissue. The stress is applied externally, such as by manual pressure or by acoustic pressure. Strain or strain rate are detected for generating an elasticity image. Altered stiffness regions may be identified. However, strain is relative or qualitative. For example, different amounts of applied stress result in different amounts of strain. The amount of applied stress may be unknown or difficult to determine accurately.